Telephoto lens system

ABSTRACT

The present invention relates to photographic lens systems and more particularly, to a telephoto lens suitable for small size cameras for which the telephoto ratio is minimized and various aberrations are corrected favourably.

/i o i n; A United States 4 a t u 11 3,838,911 Ikeda Oct. 1, 1974 [541 TELEPHOTO LENS SYSTEM FOREIGN PATENTS OR APPLICATIONS Inventor: i gi lkeda, yo Japan 28.070 9/1910 Japan 350/223 [73] Assigneez Olympus optical Co. Ltd. 696.l67 8/1953 Great Britain 350/223 Tokyo-to, Japan 22 d: A 24, Primary Examiner-John Corbin 1 I 6 pr Attorney, Agent, or Firm-Cushman, Darby & [2]] Appl. No.: 354,112 Cushman [30] Foreign Application Priority Data July 3, i972 Japan 47-66514 [57] ABSTRACT I The present invention relates to photographic lens sys- [52] US. Cl. 350/223, 350/ 176 tems and more particularly to a telephoto lens suit [51] Int. Cl. G02b 9/34, G02b 13/02 able for Small Size cameras for which the telephoto [58] Field 0! Search 350/223, i76 ratio is minimized and various aberrations are con [56] References Cited meted favourably.

UNITED STATES PATENTS 2 Claims, 9 Drawing Figures 3,459,469 8/1969 Takahashi 350/223 I PAIEN -3'.aa8.s11

FIG. I'

n r2 n I'a r9 d 3 d: sd'r da FIG. 20 FIG. 2b FIG. 20 FIG. 2a

0 m a w T 9 6 2 R m n m a M 0 5 Mm o 5 M 0 M 9A 6 m 1 0 \Jm T A A 5 6 3 5 W H L. m gllllllo EN m d sw N Lw T l A 5 WA mu PAIEN'IEDBBT H 3.888.911

saw ans 2 FIG. 30 FIG. 3b FIG. 3c FIG. 3d

SPHERICAL SINE ABERRATION CONDITION ASTIGMATISM DISTORTION 7 H14 {gm {5* 6 #9 /9 A3 Am dd- TELEPHOTO LENS SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to photographic lens systems and more particularly, to a compact telephoto lens suitable for small size cameras.

2. Description of the Prior Art For telephoto lenses, it is desirable to minimize the telephoto ratio (the distance from the first surface of the lens system to the back focus divided by the total focal length of the whole lens system) and, at the same time, to correct aberrations favourably. When, however. the telephoto ratio is made smaller, it becomes more difficult to correct aberrations.

SUMMARY OF THE INVENTION It is, therefore, a principal object of the present invention to provide a telephoto lens for which the telephoto ratio is minimized and, at the same time, various aberrations are corrected favourably.

The telephoto lens according to the present invention comprises the following four lenses. That is, the first lens is a positive lens, the second lens is a cemented lens comprising a positive lens and negative lens or a combined positive meniscus lens for which two lenses are arranged with a very small airspace between each other. the third lens is a negative meniscus lens, the fourth lens is a positive meniscus lens and a stop is arranged between the second and third lenses. Besides, the telephoto lens of the present invention satisfies conditions as listed below when reference symbol d represents the airspace between the second and third lenses, reference symbol d represents the airspace between the third and fourth lenses, reference symbols r r r and r respecitvely represent radii of curvatures of the cemented surface of the cemented second lens and of the respective surfaces of the third and fourth lenses, reference symbols n and n respectively represent refractive indexes of the front positive lens and rear negative lens of the cemented second lens, and reference symbol f represents the total focal length of the lens system as a whole.

n n 0.05, n n )f/ |r,| 0.1 4.

For the lens system according to the present invention, the above condition l) is required for favourably correcting chromatic aberration and offaxial aberrations. If the condition (I) is not satisfied. i.e., in case ofa 0.l2for |d d l 0.lf, it becomes impossible to correct astigmatism and coma by minimizing the telephoto ratio. Besides, it becomes difficult to balance aberrations over the whole field angle. This condition also serves to minimize lateral chromatic aberration and spherical aberration for every wavelength in cooperation with the other conditions. The condition (2) is required to minimize the telephoto ratio and, at the same time, to favourably correct spherical aberration and offaxial aberrations. In case of 0.25f 2r it may be advantageous for making the telephoto ratio small, but offaxial aberrations become unfavourable. In case of 2r, r the telephoto ratio cannot be made small. Besides, in case of r.; 1.2f, satisfactory symmetry of coma cannot be achieved and it becomes impossible to correct coma even when the other factors are changed.

The condition (3) is established mainly for correcting chromatic aberration and offaxial aberrations favourably. In case of l.3r r lateral chromatic aberration becomes unbalanced when the telephoto ratio is made small. In case of r, 2f, it becomes difficult to correct flare caused by coma.

The condition (4) is required for favourably correcting spherical aberration and offaxial aberrations. In case it is n;, n 0.05, zonal spherical aberration increases and. moreover, it becomes inconvenient to correct coma. lfit is l r,| (n n )flO.lf, it becomes difficult to eliminate flare caused by coma for every wavelength.

In the following, the above-mentioned telephoto lens of the present invention is described according to the illustrated embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I shows a sectional view of the embodiments of the telephoto lens according to the present invention;

FIG. 2a through FIG. 2d show graphs illustrating aberration characteristics of the embodiment l of the present invention; and

FIG. 3a through FIG. 3d show graphs illustrating aberration characteristics of the embodiment 2 of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Numerical data of the embodiments of the present invention shown in FIG. I are as given below.

Embodiment 1 .1, 4.40 n. 1.6204! v, 60.2 r, 355.454

- d 5.l9 n l.48749 v, 69.8 r 2 d l.77 n l.76l 82 v 26.5 r,= 74.890

d, l4.9l r 79.258

d L79 n, 1.66998 v, 39.3 r l7.670

d I4.70 r,.= 33.946

41,. 2.52 n; 1.805l8 v, 25.4 r,= 62.394

F l 3.57: f=

Embodiment 2 d. 3.l8 n, l.6204l v, 60.2 a:

d 5.8l r, 30.358

4, 4.84 n, l.48749 v, 69.8 r; 55l.36

d 2.26 N, l.76l82 v, 26.5 r; 65.822

d, 19.25 r. SL530 d, 1.84 n, =l.67790 v 55.3

-Continued l-mhodiincnt I r; l7.37l

d,.= '..l2 n 1.78472 v;=25.6 r, 52.334 F l :4 f= I In the above numerical data, reference symbols r through r represent radii of curvatures of respective surfaces of lenses, reference symbols d through d,, represent thicknesses of respective lenses and spaces between lenses, reference symbols n through u represent refractive indexes of respective lenses. reference symbols 11, through :1 represent Abbes numbers of respective lenses.

FIG. 2a through FIG. 2d show aberration characteristics curves for the embodiment l of the telephoto lens according to the present invention. FIG. 2a shows spherical aberration, FIG. 2b shows the sine condition, FIG. shows astigmatism and FIG. 2d shows distortion. FIG. 3a through FIG. 3d show aberration characteristics curves for the embodiment 2 of the present invention. FIG. 3a shows spherical aberration, FIG. 3b shows the sine condition, FIG. 3c shows astigmatism and FIG. 3d shows distortion.

As it is evident from the above-mentioned graphs of aberration characteristics curves of the embodiments l and 2, the present invention provides a telephoto lens for which the telephoto ratio is minized and various aberrations are corrected quite favourably.

I claim:

1. A telephoto lens system comprising a first lens, a second doublet lens, a third lens and a fourth lens, wherein said first lens is a positive lens, said second doublet lens is a cemented positive lens comprising positive and negative lenses, said third lens is a negative meniscus lens and said fourth lens is a positive meniscus lens, and said telephoto lens system having the following numerical data:

d, 4.40 n, 1.62041 v, 60.2 r, 35545 where reference symbols r through r9 represent radii of curvatures of respective surfaces of lenses, reference symbols (1, through d represent thicknesses of respective lenses and spaces between lenses, reference symbols n, through n5 represent refractive indexes of respective lenses, reference symbols 1/, through 11,-, represent Abbe's numbers of respective lenses.

2. A telephoto lens system comprising a first lens, a second doublet lens, a third lens and a fourth lens, wherein said first lens is a positive lens, said second lens is a cemented positive lens comprising positive and negative lenses, said third lens is a negative meniscus lens and said fourth lens is a positive meniscus lens, and said telephoto lens system having the following numerical data:

4,, 4.84 11, l.48749 v, 69.8 r, 551.36

a, 2.26 n, 1.76182 v, 26.5 r, 65.822

d, 1.84 n, 1.67790 v. 55.3 r, 17.371

4,. 2.12 n, =1.7s472 v, 25.6 r, 52.334

where reference symbols r through r represent radii of curvatures of respective surfaces of lenses, reference symbols d, through d, represent thicknesses of respective lenses and spaces between lenses, reference symbols n through n represent refractive indexes of respective lenses, reference symbols 1/, through 1/ represent Abbes numbers of respective lenses. 

1. A telephoto lens system comprising a first lens, a second doublet lens, a third lens and a fourth lens, wherein said first lens is a positive lens, said second doublet lens is a cemented positive lens comprising positive and negative lenses, said third lens is a negative meniscus lens and said fourth lens is a positive meniscus lens, and said telephoto lens system having the following numerical data:
 2. A telephoto lens system comprising a first lens, a second doublet lens, a third lens and a fourth lens, wherein said first lens is a positive lens, said second lens is a cemented positive lens comprising positive and negative lenses, said third lens is a negative meniscus lens and said fourth lens is a positive meniscus lens, and said telephoto lens system having the following numerical data: 